1. Field of the Invention
The present invention relates to technology for notifying the occurrence of a failure when failure occurs on an access line connected with a network.
2. Description of the Related Art
In the past, using an MPLS (Multiprotocol Label Switching) network of a service provider (SP) between a certain customer site and another customer site, VPWS (Virtual Private Wire Service) is known as a service for performing point-to-point data communication via a layer 2 VPN (Virtual Private Network).
FIG. 10 is an explanatory drawing showing an example of a network for which a typical VPWS is used. As shown in FIG. 10, with VPWS, there is an MPLS network between the User 1 which is one customer site and the User 2 which is the other customer site (following, called the VPWS network). Of these, for the one customer site User 1, the network devices such as a switch, router, and the like at the edge part of this (hereafter called the customer edge) CE1 and for the VPWS network, the network devices such as a switch, router, and the like at the other edge part (hereafter called the provider edge) PE1 are connected using an access line, and similarly, for the other customer site User 2, the customer edge CE2 at the edge part, and for the VPWS network, the provider edge PE2 at the other edge part are also connected using an access line. Then, the mutual access lines that connect between CE and PE (in other words, the provider edges PE1 and PE2) are connected point-to-point by an affiliated virtual circuit VC within the VPWS network.
For a VPWS network with this kind of constitution, for example, a layer 2 packet sent from one customer site User 1 is transferred to the provider edge PE1 via the access line from that customer edge CE1, and next, this is transferred to the provider edge PE2 via the virtual circuit VC from the provider edge PE1, and furthermore, is transferred to the customer edge CE2 via the access line from the provider edge PE2, and is received by the other customer site User 2. At this time, the layer 2 packet is encapsulated within the virtual circuit VC and transferred.
So then, for this kind of VPWS network, when building a so-called redundant structure, a structure for which a substitute path is prepared in case of network failure, for example with layer 2, by operating STP (Spanning Tree Protocol) that is the redundancy control protocol between the customer edges (CE1-CE2), it is possible to realize a redundant structure, and with layer 3, by operating the routing protocol that represents the OSPF (Open Shortest Path First) or BGP (Border Gateway Protocol), and at each customer edge, by setting the normal path and the redundant path, it is possible to realize a redundant structure.
FIG. 11 is an explanatory drawing showing an example of a network for which a redundant structure is built for the VPWS network. In FIG. 11, PE3 and PE4 are both provider edges, and these provider edges PE3 and PE4, the same as with the provider edges PE1 and PE2, within the VPWS network, these are connected point-to-point by an affiliated virtual circuit VC. Then, the redundant path that is a substitute path is constituted using CE1-PE3-PE4-CE2. As an item related to this type of technology, in the past, the item noted in Japanese Patent Laid-Open Gazette No. 2003-298632 is known, for example.
For the concerned redundant structure, within the normal path of CE1-PE1-PE2-CE2, when failure occurs, when the customer edges CE1 and CE2 detect this, by switching from the normal path to the redundant path, it is possible to keep continuity of the communication.
However, in this way, when the redundant structure is realized at the VPWS network, there were the following kinds of problems. For example, at the access line between CE1 and PE1, when failure occurs, at the customer edge CE1, since there is failure at its own access line, it is possible to detect that failure occurrence, and to immediately switch to the redundant path, but with the other customer edge CE2, since there is failure at the other party access line, to detect the failure with the aforementioned redundancy control protocol, the timeout time stipulated in the redundancy control protocol is required, so there was the problem that it was not possible to immediately switch to the redundant path.
In light of this, in the prior art, to detect failure occurrence at the other party access line, a reachability verification protocol was operated between the customer edges (between CE1 and CE2). Specifically, between the customer edges (between CE1 and CE2), an echo packet stipulated by that protocol is sent and received, for example when failure occurs at the access line between CE1 and PE1, the echo packet from the customer edge CE1 is stopped, and at the customer edge CE2, by detecting the timeout of that echo packet, that failure occurrence is detected.